Transcription

1 The Binding Problem Objects have different features such as color, shape, sound, and smell. Some, such as color and sound, are represented separately from the instant they hit our sensory receptors. Other features, such as color and shape, are initially encoded together but subsequently analyzed by separate areas of the brain. Despite this separation, in perception the brain must represent which features belong to the same object. This is the binding problem. Any case of the brain representing as associated two features or stimuli that are initially represented separately can be called binding, but this entry will focus on a subset of these: the pairing of features that belong to a common object. Solutions to the spatial binding problem A simple solution to the binding problem is to have a single neuron (or other representational unit) for each possible combination of features. However, considering that different feature dimensions such as color, shape, and texture may each have hundreds of values, it is impractical to dedicate a unit to each combination. Still, the visual system does contain neurons selective for certain combinations of features, and these may suffice to solve the binding problem in certain cases (Risenhuber & Poggio 1999). Wolf Singer has championed the theory that binding is represented via synchronous rhythmic firing of the neurons selective for the paired features (von der Malsburg 1981; Gray et al. 1989). The idea is that the joint activity of the feature representations allows other brain areas to process the features together, to the exclusion of features belonging to other objects. Groups of neurons in many parts of the brain frequently do synchronize their responses, and attention to visual stimuli can enhance the effect, but the precise relationship of the phenomenon to perceptual binding remains unclear (Fries et al. 2001; Thiele & Stoner 2003; Dong et al. 2008). For experimental psychology researchers, two papers on binding by Anne Treisman in the 1980s set the course for nearly two decades (Treisman & Gelade 1980; Treisman & Schmidt 1982). Treisman s "feature integration theory" (FIT) became not only the most influential theory of binding, but also the most influential theory of attention. FIT posits that binding is accomplished by an act of selective attention and has three elements. 1

2 1) Features like color and shape are represented separately in the brain, but for each feature (such as red) there is a feature map indicating the location of each instance of the feature in the visual field. By virtue of the position of the units that represent the feature relative to the others in the map, a location tag is implicitly included and activity of a unit signals both feature identity and location. 2) The objects of a visual scene initially cause representations of the various features of all the objects to become active. The system does not yet represent which features belong to the same object. 3) Binding happens when attention is directed to a particular location. The neurons corresponding to this location in each feature map become active to the exclusion of those in other locations, and the features occupying the location are bound. Spatial Binding: Evidence The results of thousands of visual search (see also visual search) experiments have been interpreted in the framework of FIT. In one case people were tested on the time needed to find a red X target stimulus among a large array of red O 's and blue X 's. Because the target is defined by the combination of color and shape, the task requires binding of these features. If there were no binding to determine whether any instances of red were in the same location as the X shape, the target could not be found. Searches that require binding are usually more timeconsuming than searches for a target containing a feature different from those of all the other items. In this latter case, a feature map alone is sufficient to solve the task. According to FIT, the reason for the greater difficulty in the binding search is that the binding step takes time and can only be performed in one location at a time. Attention is hypothesized to visit each location in turn, binding its features until the target is found. FIT has been useful for explaining visual search results, however a number of other models, models without any role for attention in binding, can also explain visual search performance (Rolls & Deco 2002; Eckstein 1998). These alternative models imply that the nature of the binding process cannot be determined from visual search results alone. Visual search results are affected by many factors such as image segmentation mechanisms, local salience processing, and crowding, making it difficult to isolate the binding process. 2

3 In experiments relying on fewer assumptions, Treisman documented clear binding mistakes with simple displays, in a phenomenon she called "illusory conjunctions" (Treisman & Schmidt 1982). In one illusory conjunctions experiment, two black digits and three colored letters were flashed briefly on the screen. Participants attempted to report the digits and the letters and the letters associated colors. They usually reported the correct letters and colors, but occasionally with the wrong pairing. Treisman suggested that the short presentation duration, in combination with the attentional demands required to also report the digits, meant that the attention available was sometimes inadequate to correctly bind the features. Subsequent work verified that illusory conjunctions are perceptual errors rather than an artifact of guessing strategies (Ashby, Prinzmetal & Maddox 1996), and illusory conjunctions clearly are more common when perceptual demands are high, but it remains unclear whether this reflects a critical role for attention or instead just that binding requires additional sensory processing beyond that required for identifying the features. To probe the role of attention more directly, Jochen Braun & colleagues devised a quantitative measure of the attentional resources shared by two tasks (Braun, Koch, Lee & Itti 2001). Results from this paradigm indicate that contrary to FIT, some feature bindings are perceived at little or no cost to attentionally demanding visual tasks. For example, accuracy in reporting the orientation and color of two line segments in the periphery was almost completely unaffected by the demands of a concurrent task of searching for a T among L s or an L among T s. Results from Braun's paradigm do however support the idea that attention is critical for linking features to particular spatial locations. Ability to judge the spatial configuration of adjacent red and green patches (whether red is left of green or right of green) traded off linearly with performance in concurrent central tasks, supporting a critical role for attention. Interestingly, other discriminations that may also rely on configuration do not show this property, for instance discrimination of face gender or identity (Reddy et al. 2004). Apparently the binding required for certain discriminations can proceed with little to no attention. However, even when full attention and extensive processing time is available, binding can fail profoundly, as described in the next section. Location Tagging of Features: A Prerequisite for Binding? 3

4 In her Feature Integration Theory, Treisman suggested that bindings between features are mediated by the features links to a location in common. Psychophysical demonstrations of binding failures under conditions of full attention provide support for this idea that binding is accomplished through common location tags. In a display devised by Steven Shevell et al. (2008), two separate objects are presented at the same location but in different eyes. For example a vertical array of orange and gray stripes is presented in one eye, and a horizontal array of gray and blue stripes in the other eye. The conflict between the eyes causes experience to alternate between various percepts including some involving misbinding of the color and form features. Specifically, arrays of orange with blue stripes of either orientation are perceived. This phenomenon suggests that pairing of features is not fully resolved until after the representations of the two eyes come together. That presentation of multiple instances of a feature in a single location can confound binding supports the notion that binding relies on location tags. Even when features are perceived in their correct locations, binding can still fail profoundly. Still, this too may reflect a location tagging failure that arises when the spatial scale of analysis of one feature is larger than that of another, allowing the location tag of the larger feature to correspond to more than one instance of the smaller feature. In a display devised by Hugh Wilson and Frances Wilkinson (1998), a pair of dots defines a local orientation. Hundreds of such pairs of dots are scattered across the screen and oriented such that globally, a spiral is perceived. If all these dots are white and unrelated black dots are randomly interspersed with them, then under brief presentation conditions binding fails utterly - people are unable to say whether the dots forming the clearly-visible shape are black or white. This phenomenon suggests that the mechanisms for a feature (here, shape) extracted by combining a number of local components does not preserve information about other aspects of its constituents (here, color). Rather, the global shape is assigned to a large area, with multiple colors tagged with locations within it. Rare neuropsychological syndromes further highlight the role of location tagging. Some patients with bilateral parietal damage mispair color and shape much more frequently than they misperceive the constituent features (Friedman-Hill et al. 1995). Damage to the pulvinar, a 4

5 subcortical structure, can cause similar binding problems (Ward et al. 2002). Both disorders are accompanied by a deficit for localization of even an isolated feature, consistent with the thesis that binding of visual features is accomplished through common location tags. Temporal Binding Certain binding failures documented in healthy observers suggest that the binding process is quite slow relative to feature identification. Two dot patterns, each forming a different global shape (like those mentioned earlier), each a single color (e.g. red or green) were set in alternation (Clifford, Holcombe & Pearson 2002). The two shapes were constructed such that their shapes could not be determined when the alternation rate exceeded the temporal resolution of the shape identification mechanism. The two global shapes were easily perceived at 15 Hz, implying rapid grouping of the dot pairs and extraction of the global shape, and the color of each dot was perceptually obvious. However, without extensive scrutiny, observers were unable to determine which shape was formed of green dots and which shape formed of red dots unless the patterns alternated slower than 3 Hz. Binding of color and motion also shows a slow limit of less than 3 Hz, even when both features are local (Moradi & Shimojo 2004; Arnold 2005). The alternation of colors and motions causes the display to contain more than one feature of each type in a single perceptual location. With binding based on location tags, this yields binding ambiguity when the displays are alternated fast enough to exceed the temporal resolution of the binding process. The 3 Hz result indicates that binding is slow and requires much more time than does identification of the constituent features. Even at slow rates, binding of the features that occur together in time may pose problems beyond those faced by spatial binding. For spatial binding, linking features based on common location works well thanks to the large number of spatially organized areas in the visual system. In contrast, no chronotopically-organized visual areas have been found, raising the issue of how features might be tagged temporally. Temporal tagging would be unnecessary if all features were processed in the same amount of time. But features have different sensory latencies and processing times (Schmolesky et al. 1998). Perhaps the perceptual systems have a scheme for tagging the time that features actually occurred in the world, as opposed to when they are identified by the brain (Nishida & Johnston, in press), but this is not yet understood. 5

PSYCHOLOGICAL SCIENCE Research Article The Capacity of Visual Short- Term Memory Is Set Both by Visual Information Load and by Number of Objects G.A. Alvarez and P. Cavanagh Harvard University ABSTRACT

Chapter 6: Visual Attention "Everyone knows what attention is. It is the taking possession by the mind in clear and vivid form, of one out of what seem several simultaneously possible objects or trains

Motion Perception The perception of motion is a key element of visual perception since both objects in the environment and the observer can move. Motion perception is essential to muscle control and movement.

Visual area responds to local motion MST a Visual area MST responds to optic flow MST a Visual area STS responds to biological motion STS Macaque visual areas Flattening the brain What is a visual area?

Basic Architecture of the Visual Cortex A.L. Yuille (UCLA) The Retina and the Cortex. Basic Biology. With about 10 million retinal receptors, the human retina makes on the order of 10 to 100 million measurements

The Physiology of the Senses Lecture 3: Visual Perception of Objects www.tutis.ca/senses/ Contents Objectives...2 What is after V1?...2 Assembling Simple Features into Objects...4 Illusory Contours...6

Masters research projects 1. Adapting Granger causality for use on EEG data. Background. Granger causality is a concept introduced in the field of economy to determine which variables influence, or cause,

Chapter 4 The Scientific Data Mining Process When I use a word, Humpty Dumpty said, in rather a scornful tone, it means just what I choose it to mean neither more nor less. Lewis Carroll [87, p. 214] In

Long-term Memory for 400 Pictures on a CommonTheme Stine Vogt a* and Svein Magnussen, a,b a Department of Psychology, University of Oslo, Norway b Centre for Advanced Study, The Norwegian Academy of Science

A model of memory, learning and recognition Bruce Hoeneisen Universidad San Francisco de Quito 6 May 2002 Abstract We propose a simple model of recognition, short-term memory, longterm memory and learning.

Color Perception Color vision is a key aspect of perceptual organization. It can be useful for detecting objects against a background. Color is related to wavelength. The perceptual dimensions of color

Cognitive influences on attention In 1880, William James famously defined attention as taking possession by the mind of one out of several simultaneously possible objects or train of thoughts. The modern

RESEARCH Research Ka Chai Lo Dr. Ivo Dinov Department of Statistics/ Neuroscience Investigation of Optical Illusions on the Aspects of Gender and Age Optical illusions can reveal the remarkable vulnerabilities

-Based Group Activities for a Course David S. Kreiner University of Central Missouri Author contact information: David Kreiner Professor of Psychology University of Central Missouri Lovinger 1111 Warrensburg

Brain Function, Spell Reading, and Sweep-Sweep-Spell by Abigail Marshall, March 2005 This is not phonics or a phonetic process; it is simply letter and word recognition. Ronald D. Davis T wo of the most

ITS 102: Visualize This! Lecture 1: The Visual System Klaus Mueller Computer Science Department Stony Brook University The Visual Brain Over 50% of the human brain is dedicated to vision and visual representations,

Visualizing Multidimensional Data Through Time Stephen Few July 2005 This is the first of three columns that will feature the winners of DM Review's 2005 data visualization competition. I want to extend

AP Psychology 2012 Scoring Guidelines The College Board The College Board is a mission-driven not-for-profit organization that connects students to college success and opportunity. Founded in 1900, the

Chapter 14: The Cutaneous Senses Skin - heaviest organ in the body Cutaneous System Epidermis is the outer layer of the skin, which is made up of dead skin cells Dermis is below the epidermis and contains

CHAPTER 6 PRINCIPLES OF NEURAL CIRCUITS. 6.1. CONNECTIONS AMONG NEURONS Neurons are interconnected with one another to form circuits, much as electronic components are wired together to form a functional

Human Cognition An important foundation for the design of interfaces is a basic theory of human cognition The information processing paradigm (in its most simple form). Human Information Processing The

AQT-D A Quick Test of Cognitive Speed AQT-D is designed for dementia screening. A General Introduction to AQT AQT 1 is an objective, reliable and standardized screening test designed to measure cognitive

Clinical Neuropsychology. Recovery & Rehabilitation Alan Sunderland School of Psychology 1 The Changing Role of Clinical Neuropsychology HISTORY The Origins of Clinical Neuropsychology Emergence as a profession

Visualization Viewpoints Editor: TheresaMarie Rhyne Toward a Perceptual Theory of Flow Visualization Colin Ware University of New Hampshire What constitutes good visualization research? Are researchers

History of eye-tracking in psychological research In the 1950s, Alfred Yarbus showed the task given to a subject has a very large influence on the subjects eye movements. Yarbus also wrote about the relation

Processing the Image or Can you Believe what you see? Light and Color for Nonscientists PHYS 1230 Optical Illusions http://www.michaelbach.de/ot/mot_mib/index.html Vision We construct images unconsciously

The Parietal Lobes Functions of the Parietal Lobes The Parietal Lobes develop at about the age of 5 years. They function to give the individual perspective and to help them understand space, touch, and

The Cheshire Cat Illusion The Cheshire Cat vanished quite slowly, beginning with the end of the tail, and ending with the grin, which remained some time after the rest of it had gone. - Alice s Adventures

A Short Introduction to Computer Graphics Frédo Durand MIT Laboratory for Computer Science 1 Introduction Chapter I: Basics Although computer graphics is a vast field that encompasses almost any graphical

CONTE Summer Lab Experience Application When preparing your application for funding from the CONTE Summer Lab Experience through the Undergraduate Program in Neuroscience, please read these instructions

How do we perceive our environment? Complex stimuli are broken into individual features, relayed to the CNS, then reassembled as our perception Sensation and Perception Terminology Stimulus: physical agent

Objectives 0 Participants will be able to identify 4 characteristics of a healthy brain. 0 Participants will be able to state the functions of the brain. 0 Participants will be able to identify 3 types

Feature Story 1105 Playing Tricks On The Mind s Eye Seeing isn t believing. These visual illusions play havoc with our brains as it seeks to interpret what is sees. Seeing isn t believing. If you think

Brain Maps The Sensory Homunculus Our brains are maps. This mapping results from the way connections in the brain are ordered and arranged. The ordering of neural pathways between different parts of the

2012 Psychology GA 1: Written examination 1 GENERAL COMMENTS This examination was the final Unit 3 June examination for the VCE Psychology Study Design. From 2013, a single examination covering both Units

Perception and Mind-Dependence Lecture 4 1 Last Week The Argument from Illusion relies on the Phenomenal Principle. The Phenomenal Principle is motivated by its ability to explain the sensuous character

University of Edinburgh College of Science and Engineering School of Informatics Informatics Research Proposal supervised by Dr. Sethu Vijayakumar Optimized bandwidth usage for real-time remote surveillance